During the drilling, stimulation, completion, and production phases of wells for petroleum or water extraction, the subterranean use of compositions having high viscosities is important for a wide variety of purposes. Higher viscosity fluids can more effectively carry materials to a desired location downhole, such as proppants or drill cuttings. The use of higher viscosity fluids during hydraulic fracturing generally results in larger more dominant fractures. Higher viscosity drilling fluids can more effectively carry materials away from a drilling location downhole.
One common way to attain high viscosities in drilling fluids is to use a mixture of water and a viscosifier. However, typically viscosifiers must be added in high concentrations to provide viscosities sufficient to suspend a desired proppant or to suspend drill cuttings, which can result in high transportation costs and low efficiency preparation of viscous materials. The higher temperatures experienced in subterranean formations can limit, reduce, or degrade the effectiveness of certain viscosifiers, resulting in the use of larger amounts of viscosifiers to compensate for the high temperatures, or the use of expensive temperature-resistant viscosifiers. In addition, the presence of certain ions in water can limit, reduce, or degrade the effectiveness of certain viscosifiers. This limits the use of certain ion-containing water, such as sea water, or water recovered from or naturally produced by some subterranean formations. As a result, the oil and gas industry spends substantial amounts of money and energy to use large amounts of viscosifiers to compensate for the salt sensitivity, obtain expensive salt-resistant viscosifiers, obtain fresh water used for drilling fluid or fracturing fluid applications, or to avoid formations having substantial concentrations of particular ions.
Various viscosifiers are used with clay in order to achieve a desired viscosity or degree of fluid loss control. However, the use of clay can cause severe formation damage due to plugging of the pores of the reservoir formation and due to difficulty of clean-up.
Polyacrylamides crosslinked with methylenebisacrylamide are incompatible with calcium carbonate bridging agents after aging due to hydrolysis of the amides to form polyacrylate, causing precipitation of the calcium carbonate and the polymer. In addition, methylenebisacrylamide can be hydrolyzed with aging, causing loss of viscosity and fluid loss control.